Carrier Aggregation
The 3rd Generation Partnership Project (3GPP) Long Term Evolution (LTE) specifications standardized Carrier Aggregation (CA) supporting Component Carrier (CC) bandwidths up to 20 MHz, which is the maximal LTE Rel-8 carrier bandwidth. Hence, an LTE operation wider than 20 MHz is possible and appear as a number of LTE carriers to an LTE terminal. An example of CA is illustrated in FIG. 1.
The 3GPP LTE standard supports up to 5 aggregated carriers where each carrier is limited in the Radio Frequency (RF) specifications to have one of six bandwidths, namely, 6, 15, 25, 50, 75 or 100 Resource Blocks (RB) corresponding to 1.4, 3, 5, 10, 15 and 20 MHz, respectively.
The number of aggregated CCs as well as the bandwidth of the individual CC may be different for uplink and downlink. A symmetric configuration refers to the case where the number of CCs in downlink and uplink is the same whereas an asymmetric configuration refers to the case that the number of CCs is different.
During initial access an LTE terminal operates on one carrier only. Upon successful connection to the network a terminal may, depending on its own capabilities and the network, be configured in Radio Resource Control (RRC) signalling with additional CCs in the Uplink (UL) and Downlink (DL). The 3GPP radio specifications, in example, 3GPP 36.101 v10.17.0, includes requirements for up to 2 CC DL and only 1 UL in Rel-10. In the Rel-12 version of this specification, 3 DL CA are being introduced as well as UL inter-band CA.
Wireless Device (e.g., UE) Radio Network Related Capability Information
The purpose of this procedure is to transfer UE radio access capability information from the User Equipment (UE) to Evolved Universal Mobile Telecommunications System Terrestrial Radio Access Network (E-UTRAN). If the UE has changed its E-UTRAN radio access capabilities, the UE shall request higher layers to initiate the necessary NAS procedures, as described in 3GPP TS 23.401 v10.13.0, section 5.11, which would result in the update of UE radio access capabilities using a new RRC connection.
To allow for a range of user equipment (UE)/wireless device implementations, different wireless device capabilities are specified. The wireless device capabilities may be used by the network to select a configuration that is supported by the wireless device. FIG. 2 illustrates an example of UE capability transfer.
In 3GPP standardization of E-UTRAN radio access, the UE radio network related capability information is transferred using Radio Resource Control (RRC) signalling from the UE (wireless device) to the eNode B (eNB or base station).
Information on the UE radio network related capability information has to be present in the eNB in the RRC connected state of the UE. Moreover, when a handover is made from a first/source eNB to a second/target eNB the UE capability information needs to be moved from the source eNB to the target eNB. However, in RRC idle state there is no need to maintain any information of the UE, including the UE capabilities, in the eNBs.
In order to avoid uploading the UE capabilities over the radio interface between the UE and the eNB each time the UE performs a transition to RRC connected state, for example, when the UE specific context is created in the eNB, the eNB uploads the UE capability information to the Mobility Management Entity (MME) in the Evolved Packet Core (EPC) so that it can be stored there when the UE is in RRC idle state. When the UE next time returns to RRC connected state the UE capability information will be downloaded from the MME to the eNB.
The UE radio network related capability information is grouped, where each group reflects a certain type of capabilities. Examples of such capability groups are Radio Frequency (RF) Parameters, measurement parameters, and Inter-RAT (Radio Access Technology) parameters. The RF-Parameters includes, for example, supported Evolved Universal Terrestrial Radio Access (EUTRA) frequency bands, supported EUTRA band combinations.
Measurement Parameters includes information about the UE need for DL measurement gaps while performing inter-frequency measurements when UE operating on a specific E-UTRA band or on a specific E-UTRA band combination. Inter-RAT Parameters includes information about the supported frequency bands for each other RAT the UE supports, as described in 3GPP TS 36.300, v10.12.0, section 18, and 3GPP TS 36.331, v10.15.0, section 5.6.3. In the following “UE capability” refers to the “UE radio network related capability”.
Handover Preparation Procedure
Handover preparation procedure is used to transfer the RRC information related to one UE from source eNB/source RAT to target eNB including the UE capability information. The information will be used by the target eNB to appropriately configure the UE according to the UE capability and the eNB configuration/implementation in the following handover command sent to the UE.